Several (top)riders did/do altitude camps to prepare important one-dayraces. Or to prepare a one hour effort, cfr attacking the world hour record. It makes a huge difference. Sometimes the altitude camp is ment for a good result in both a one-day race and a GT (Liège and the Giro, Clasica San Sebastian and the Vuelta and evt the worlds).Why would you do a 2-week altitude camp for one or two one-day races? It makes no sense, and is a waste of resources. What other riders are doing altitude camps?
But the problem is that the effect of a third and fourth altitude camp (long or short) within a few months is a lot smaller. Not to forget he mental burden that can partly cancel out any physical benefits. So, that is the reason that an altitude camp is rarely done to prepare the worlds and Lombardia at the end of the season. What is being done is going to altitude camp to prepare for the Vuelta and to extend the shape to the worlds. In 2022 Evenepoel already did his second trainingcamp just before the Clasica San Sebastian, going to the Vuelta a few weeks later (the Vuelta itself has the effect of a moderate altitude trainingcamp) and keeping his form till the worlds.